The proposed research project is based upon our previous observations that lymphocytes from cystic fibrosis (CF) patients with progressive pseudomonas pulmonary disease do not proliferate normally when exposed to antibiotic-killed pseudomonas in vitro. Our recent studies indicate that this defect in lymphocyte function is not due to inhibitory plasma factors or the inhibitory activity of macrophages and is most likely due to abnormalities in the lymphocyte themselves. In this project we proposed to: a) Study changes in lymphocyte subpopulations in CF patients during exacerbations and remissions from pseudomonas pulmonary infection. b) Determine if "suppressor" lymphocyte subpopulations developed in these patients. c) Identify the subpopulation characteristics and properties of these suppressor cells. d) Correlate changes in lymphocyte subpopulations and in vitro lymphocyte responses to pseudomonas to the clinical state of the patient and the progression of pulmonary disease.